Your electricity bill is high, but you have no idea where it all goes. That is the problem with electricity: you see one total and nothing else. You cannot save on something you cannot see.
There is a fix for that. You measure your use on three levels. First the total, through your smart meter and its P1 port. Then per circuit in the consumer unit, using an energy meter like the Shelly EM or Shelly Pro 3EM with current clamps around the live wires. And finally per appliance, with a simple plug-in energy monitor or a smart plug that measures.
You measure use per circuit by clipping a current clamp (also called a CT clamp) around the live wire of that circuit. The meter reads how much current runs through that wire and sends it to an app over wifi. That way you see, live, that circuit 4 (the utility room with the tumble dryer) draws far more than the rest. One warning: working inside the consumer unit is electrical work. The P1 port and the plug-in monitors are perfectly safe to do yourself.
In this article you will read exactly how each level works, what it costs, what it helps you track down and how to turn that data into a lower bill.
Why measuring per circuit pays off so well
A smart meter gives you the total for your whole house. Handy for seeing whether you used more today than yesterday, but it will not tell you which appliance is the culprit.
Measuring per circuit sits right in between. Your consumer unit is split into circuits: one for the kitchen, one for the washing machine and dryer, one for the bathroom, and so on. Measure per circuit and you see straight away which part of your house eats the most electricity. That narrows the search enormously.
Then you measure per appliance to answer the last question: is it the tumble dryer, the freezer in the garage, or that old fridge that never switches off?
The logic is simple. Measure, discover, tackle. Skip the first step and you are just guessing, and you might end up replacing an appliance that was actually efficient.
The three levels of measuring at a glance
Before we go deep, here is the full picture. Three methods, each with its own purpose.
| Level | Method | What you measure | DIY-friendly? | Indicative cost |
|---|---|---|---|---|
| Total | Smart meter + P1 port (e.g. HomeWizard P1) | Use for your whole house, live and per quarter hour | Yes, safe | Free (app) up to around 25 to 35 euros (P1 meter) |
| Per circuit | Energy meter with current clamps in the consumer unit (Shelly EM / Pro 3EM) | Use per circuit or per phase | No, electrical work inside the unit | Around 50 euros (EM) up to roughly 100 euros or more (Pro 3EM) |
| Per appliance | Plug-in kWh monitor or smart plug with metering (e.g. Shelly Plug S) | Use of a single appliance | Yes, safe | Around 10 to 30 euros each |
Prices are indications and vary by shop and by moment. But the ratio holds: you start free or cheap, and you only invest more when you genuinely want to go deeper.
Now level by level.
Level 1: measuring the total through the P1 port
Every smart meter in the Netherlands has a P1 port. It is a small socket (it looks like an old telephone connection) that you plug a reader into. Through that port your meter continuously sends out your electricity and gas use. You have a legal right to it and it costs you nothing: your grid operator is not allowed to block the port.
There are two routes.
Route 1: free, through an app. Plenty of energy suppliers and apps let you look back at your use per quarter hour, based on the data that runs through your grid operator. That is free and you do not have to install anything. The downside: that data often lags a day behind, so you do not see live what is happening right now.
Route 2: your own P1 meter. If you want live insight, you plug a reader module onto the P1 port. The best known is the HomeWizard P1 Meter, at around 25 to 35 euros. You click it onto the port, connect it to your wifi, and see in the app in real time how much your house is drawing, down to the watt.
That live insight is worth its weight in gold for the next step. You switch everything off, see what is left, then switch appliances on one by one to see what each of them does to the reading.
This level is one hundred percent safe to do yourself. You never open the consumer unit and you never go near live parts. You simply push a plug into a socket.
Level 2: measuring per circuit in the consumer unit
Now it gets interesting, and more technical too. To measure per circuit, you fit an energy meter inside your consumer unit and clip a current clamp around the live wire of every circuit you want to follow.
How a current clamp works
A current clamp (CT clamp) is a ring that you clip around a live wire. You do not have to cut the wire. The clamp measures the magnetic field around the wire and works out from that how much current is flowing through it. Simple principle, reliable result.
The energy meter itself usually sits on the DIN rail (the same rail your breakers are mounted on) and sends the readings to an app over wifi.
Which energy meter to choose
Two options keep coming up:
Shelly EM. This one has two inputs, so you can measure two circuits or two parts of your installation. It costs around 50 euros, plus roughly 10 euros for an extra clamp. Fine if you want to keep an eye on a couple of suspect circuits.
Shelly Pro 3EM. This one measures three channels at once with three current clamps. Ideal if you have a three-phase supply (a clamp on each phase) or if you want to follow several circuits at the same time. Budget roughly 100 euros or more. The Pro models mount on the DIN rail and can also communicate over a network cable.
If you want to see exactly how your house is balanced across the phases, or you are working with solar panels or a home battery, then measuring per phase with a 3EM meter is the logical choice.
SAFETY: this is electrical work
Here I have to be strict. Fitting a current clamp around a live wire means working inside the consumer unit, right next to parts that carry mains voltage. You only do that with the power off: main switch out, and check that there really is no voltage left.
Not a hundred percent sure of what you are doing? Then have a qualified electrician do it. A wrongly connected meter is not just inaccurate, it can be dangerous. The meter costs you a tenner or two, a mistake in your consumer unit can cost you far more. The plug-in monitors from level 3 often give you 80 percent of the insight without ever opening the unit.
Level 3: measuring per appliance with a plug-in monitor
This is the level most people start with, and rightly so. It is cheap, safe and gives you an immediate answer to the question: how much does this one appliance actually use?
The plug-in kWh monitor. A small box you put between the wall socket and your appliance’s plug. On a little display you read off the power (watts) and the use over time (kWh). Often only 10 to 25 euros. Leave it on your fridge or freezer for a week and you know exactly what that appliance costs per year.
The smart plug with metering. Same function, but with wifi and an app. Examples are the Shelly Plug S or the HomeWizard Energy Socket, usually somewhere between 15 and 30 euros. The advantage: you read it remotely in an app, you see graphs over time, and you can often switch the appliance on and off remotely as well. Handy for appliances that quietly sit on standby.
Both are completely safe. You push a plug into a socket, that is all. For most households this level is the fastest route to a concrete result.
Which appliances use a lot of electricity?
Now the key question: what are you actually looking for? There is one simple rule of thumb that tells you almost everything.
Appliances that make heat are the big users. Heating costs an enormous amount of energy. Anything with a heating element (a water heater, a dryer, an electric heater) draws far more than appliances that only “think” or give light.
Below is an overview based on figures from Milieu Centraal, the Dutch consumer information organisation. The euro amounts are indicative; Milieu Centraal calculates with roughly 21 cents per kWh in their figures, so at a higher rate the costs rise accordingly. The kWh numbers are the robust comparison.
| Appliance | Order of magnitude per year | Why |
|---|---|---|
| Electric water heater (>20 litres) | up to around 1,700 kWh | Keeps water hot continuously |
| Underfloor heating pump (old, no switch) | around 700 kWh | Runs day and night |
| American-style fridge | around 370 kWh | Large, cools non-stop |
| Old fridge-freezer (15 years) | around 350 kWh | Poor insulation, always running |
| Small under-sink water heater | around 300 kWh | Small but constantly hot |
| Dishwasher | around 230 kWh | Heats water every cycle |
| Tumble dryer | around 180 kWh | Heats air (condenser dryer) |
| New efficient fridge-freezer (C label) | around 160 kWh | For comparison: less than half |
A few things stand out.
That electric water heater is the outright champion. Nearly 1,700 kWh a year, which is a hefty chunk of an average annual bill in a single appliance.
An old fridge or freezer easily uses twice as much as a new efficient model. The difference between 350 and 160 kWh is almost 200 kWh a year. An appliance like that runs 24 hours a day, so every saving there keeps ticking over continuously.
And watch out for hidden users like that old underfloor heating pump: 700 kWh a year for something you never think about. Exactly the kind of thing you track down by measuring per circuit.
From measuring to saving: what to do with the data
Measuring is fun, but it is about what you do with it. Here is how you turn numbers into a lower bill.
Track down your phantom load
Try this test. In the evening or at night, switch off everything you can. Then look at your P1 meter or energy meter to see what is still being used. Whatever is left is phantom load: appliances drawing power while you are not using them.
Think of TVs on standby, chargers left in sockets, the wifi router, set-top boxes, a gaming PC in sleep mode. In an average household this adds up to around 450 kWh a year, according to Milieu Centraal. That is money disappearing while you sleep.
The fix: put appliances you do not need running constantly on a switched extension lead or on a smart plug that shuts them off automatically. That cuts the phantom load away without you having to think about it again.
Tackle the biggest user first
If your measurements show one appliance standing out, start there. An old freezer in the garage drawing 350 kWh a year while it sits half empty? Switching it off or replacing it pays back straight away. A water heater keeping water hot all night that you never use? Look at a timer or a more efficient alternative.
Do the payback maths
Stay level-headed. Recouping a few hundred euros for a new efficient fridge on a saving of 190 kWh (roughly 50 to 60 euros a year) quickly takes five years or more. As long as your old appliance still works, replacing it purely for the energy is often not worth it. But if a replacement is coming up anyway, pick the most efficient label.
A 15-euro plug-in monitor that finds you one power hog, on the other hand, pays for itself in a few months. That cheap measuring step almost always pays off.
Make the most of dynamic tariffs
If you have a dynamic energy contract, the price changes by the hour. With live insight from your P1 meter you can run the big users (washing machine, dryer, dishwasher, charging a car) during the cheap hours. Measuring gives you the data to time that cleverly.
Frequently asked questions
Can I fit an energy meter in my consumer unit myself?
Technically you can, but it is electrical work inside the consumer unit, fitting current clamps around live wires. That is only allowed with the power off, with the main switch out and after checking that there really is no voltage left. In any doubt? Have a qualified electrician do it. The plug-in monitors and the P1 port are completely safe to do yourself.
What is the difference between the P1 port and an energy meter with current clamps?
The P1 port gives you the total for your whole house and is free and safe to read. An energy meter with current clamps in the consumer unit measures per individual circuit or per phase, so you can see which part of your house uses the most. The first is your starting point, the second is for more targeted insight.
Which appliance usually uses the most electricity in the home?
Appliances that make heat. Think of an electric water heater (up to around 1,700 kWh a year), a tumble dryer, an electric heater and the dishwasher. Appliances that run day and night, like an old fridge, a freezer or an underfloor heating pump, also add up fast because they never switch off.
How much does it cost to measure my electricity use?
You can start for free with an app that shows your use via your grid operator. A P1 meter for live insight costs around 25 to 35 euros. A plug-in monitor or smart plug per appliance costs 10 to 30 euros. Measuring per circuit with a Shelly EM starts around 50 euros, a Shelly Pro 3EM sits higher. Prices vary by shop.
How do I find my phantom load?
At night, or when you are out, switch off as many appliances as you can and look at your P1 meter or energy meter to see what is still being drawn. That remainder is phantom load. In an average household it adds up to around 450 kWh a year. Tackle it with switched extension leads or smart plugs.
Does a smart plug measure as accurately as a meter in the consumer unit?
For a single appliance a good smart plug is accurate enough to show you what that appliance uses. A meter with current clamps in the consumer unit is meant for measuring whole circuits or phases, so it serves a different purpose. For most saving questions, plug-in monitors will get you a long way.
Getting started
Start small. Plug a P1 meter onto your smart meter, or put a plug-in monitor on your most suspicious appliance. Within a week you will know more about your consumption than in all the years before. From there you work your way down: from total, to circuit, to appliance, until you know exactly where your money is going.
Once you know which appliances are driving up your electricity bill, you will want to deal with them properly. Where the real savings sit without an expensive renovation, you can read in Energie Verpulveraar.